EP3700861A1

EP3700861A1 - Process and apparatus for removal of impurities from chlorosilanes

Info

Publication number: EP3700861A1
Application number: EP18792913.8A
Authority: EP
Inventors: Kai SCHILLINGER; Nena MILENKOVIC
Original assignee: Nexwafe GmbH
Current assignee: Nexwafe GmbH
Priority date: 2017-10-27
Filing date: 2018-10-19
Publication date: 2020-09-02
Anticipated expiration: 2038-10-19
Also published as: EP3700861B1; CN111263732A; WO2019081380A1; CN111263732B; JP2021500305A; JP7219494B2; US20200283298A1; US11560316B2; DE102017125221A1

Abstract

Process for removal of impurities, in particular of dopants, from chlorosilanes which comprises the following steps: (a) heating a deposition surface (3); (b) contacting the heated deposition surface (3) with at least one gaseous chlorosilane mixture, said gaseous chlorosilane mixture comprising at least one chlorosilane and at least one impurity, in particular at least one dopant; (c) at least partially removing the impurity, in particular the dopant, by forming polycrystalline silicon depositions on the deposition surface (3), said polycrystalline silicon depositions being enriched with the impurity, in particular with the dopant; (d) discharging the purified gaseous chlorosilane mixture; (e) contacting the heated deposition surface (3) with an etching gas to return the polycrystalline silicon depositions and the impurity, in particular the dopant, into the gas phase to form a gaseous etching gas mixture; and (f) discharging the gaseous etching gas mixture.

Description

Method and device for removal

of impurities from chlorosilanes

description

The production of crystalline silicon layers for solar cells and the microelectronics can be carried out, inter alia, by chemical vapor phase epitaxy of silicon on substrates, which in contrast to conventional manufacturing processes by sawing silicon blocks from the Czochralski or Zonensch melts process significantly lower layer thicknesses are achieved. Since in chemical vapor phase epitaxy, the thickness of the silicon layer formed can be controlled by a suitable choice of reaction conditions, a subsequent sawing of silicon, as is absolutely necessary with silicon blocks from the aforementioned method, is not required, whereby sawing losses can be avoided. The reduction of the layer thickness and the saw losses, made possible by the chemical vapor phase epitaxy, thus leads to a significant reduction of the production costs.

As the silicon precursor compound u u. Silanes and chlorosilanes, wherein the use of silanes due to their autoignition in contact with atmospheric oxygen is usually avoided. For thermodynamic reasons, only a small proportion of the precursor compound used in a chemical vapor deposition is generally deposited as a solid layer on a substrate. This proportion is dependent on a gas composition in the reaction chamber of the chemical vapor deposition. For example, in the production of crystalline silicon films by gas phase epitaxy using chlorosilanes as the precursor compound, such as silicon tetrachloride or trichlorosilane, only about 25% of the chlorosilane is reacted. This means that pollutants that are permanently polluting and sometimes very difficult to clean up are in the form of gaseous chlorosilane mixtures. In order to reduce process costs and to reduce these environmentally harmful wastes, it is therefore absolutely necessary, especially on an industrial scale, to purify the unused chlorosilane and to recycle it to the process. However, the problem with such a recycling of the chlorosilane is that the exhaust gas discharged from large-scale plants not only contains unused chlorosilanes and hydrogen as the process gas, but also small amounts of unused dopants and impurities. For example, dopants are present in traces of a few ppb (parts per billion) in the gaseous chlorosilane mixtures. Such low concentrations of dopants can not be sufficiently separated by conventional chlorosilane recycling, such as by means of a distillative separation apparatus with upstream gas scrubber. However, since even small concentration fluctuations of the dopants strongly affect the semiconductor properties of silicon, the concentration of the dopants in chlorosilane must be adjusted to a few ppb and impurities must be removed before the chlorosilane is fed back into the actual epitaxy process. Although such high-purity chlorosilanes are commercially available, they are very expensive to produce, which ultimately has a negative effect on the process costs of chemical vapor phase epitaxy. Relatively cheap chlorosilanes usually contain metal-containing impurities which also strongly influence the semiconductor properties of crystalline silicon layers.

Since a distillative purification of the chlorosilane mixtures is not sufficient for the removal of such impurities, for example, methods using microporous solid phase materials for removing the dopants have been proposed, which solid phase materials bind the dopants due to physical interactions and thus from a liquid or gaseous chlorosilane Remove the mixture. For example, US 471 3230 A proposes a process for removing boron-containing dopants from chlorosilanes, in which a gaseous boron-containing chlorosilane mixture is passed over a silica gel. Although this method makes it possible to reduce the boron concentration to up to 100 ppba (parts per billion atomic). When using silica gel, however, other waste materials, which must be disposed of accordingly. Furthermore, the amount of purified chlorosilane and the rate of purification are highly dependent on the properties and amount of solid phase material employed, making such a solid phase material very difficult to integrate into a large-scale cycle process. The present invention is therefore based on the object of specifying a method and a device for removing impurities, in particular dopants, from chlorosilanes, which are suitable for the purification and recycling of chlorosilanes on an industrial scale.

This object is achieved by a method having the features of claim 1 and a device having the features of claim 9.

Advantageous developments of the invention I dee are the subject of U nteransprüchen.

The invention relates to a process for the removal of impurities, in particular of dopants, from chlorosilanes according to claim 1. Furthermore, the invention relates to a device for removing impurities, in particular dopants, from chlorosilanes according to claim 9.

The process according to the invention for removing impurities, in particular dopants, from chlorosilanes comprises the following process steps:

First, in a process step (a), heating takes place from a separation surface. In a process step (b), at least one gaseous chlorosilane mixture is brought into contact with the heated deposition surface, which gaseous chlorosilane mixture comprises at least one chlorosilane and at least one impurity, in particular at least one dopant. Thereupon, in a method step (c), at least partial removal of the impurity, in particular of the dopant, by formation of polycrystalline silicon deposits on the deposition surface, which polycrystalline silicon deposits are enriched with the impurity, in particular with the dopant. In the subsequent process step (d), the purified, gaseous chlorosilane mixture is removed. In order to recycle the polycrystalline silicon deposits and the impurity, in particular of the dopant, into the gas phase, an etching gas is brought into contact with the deposition surface in a method step (e), whereby it is used to form a gaseous etching gas mixture comes. In a further method step (f), the gaseous etching gas mixture is discharged.

It is well known that the use of chlorosilanes in the chemical vapor phase epitaxy under atmospheric pressure at temperatures from 600 ° C leads to the formation of polycrystalline silicon deposits. These polycrystalline silicon deposits are unwanted byproducts in chemical vapor phase epitaxy, which include, but are not limited to: may lead to blockage of gas lines of the epitaxial chamber, which is why the epitaxy chamber and the associated gas lines must be freed regularly from these polycrystalline silicon deposits.

Investigations by the applicant have shown that impurities and dopants which are contained in the chlorosilanes can accumulate in the polycrystalline silicon deposits and can thus be removed from the chlorosilane mixtures. The reason for this is that polycrystalline silicon deposits have a multiplicity of crystal defects in which the impurities and dopants are stored or accumulated. In addition, the decomposition temperatures of common dopant compounds, in particular hydrides, in particular phosphine and diborane, are lower than those of chlorosilanes. H hereby can be trapped by a very small amount of polycrystalline silicon formed large amounts of impurities and dopants. The formed polycrystalline silicon deposits can be converted into the gas phase again together with the impurities and / or the dopants by means of an etching gas and be discharged. Thus, the process according to the invention makes it possible to remove impurities from chlorosilane mixtures without the use of further purification materials. In an advantageous embodiment of the method, in step (b) the

I n-contacting the gaseous chlorosilane mixture and the Abscheidefläche in the presence of a process gas. It is within the scope of the invention that a total amount of the gaseous chlorosilane mixture in a molar ratio of 1 to 1 0 mol% is present in the process gas. However, the invention is not limited thereto. Since the deposition rate of polycrystalline silicon is temperature-dependent and can be increased in the presence of hydrogen, hydrogen is used as the process gas in a further advantageous embodiment of the method according to the invention.

In an advantageous embodiment of the method, the purified gaseous chlorosilane mixture removed in step (d) has a residual concentration of the impurity, in particular of the dopant, less than 1000 ppb, preferably less than 100 ppb, more preferably less than 1.5 ppb. Chlorosilanes with such a low concentration of impurities and / or dopants are suitable for recycling into a corresponding epitaxy process.

In a further advantageous embodiment, the chlorosilane is tetrachlorosilane and / or trichlorosilane and / or dichlorosilane. However, it is also within the scope of the invention that higher molecular weight chlorosilanes can be used.

A further advantageous embodiment of the method provides that the formation of polycrystalline silicon deposits on the separation surface takes place at a pressure of 0.8 bar to 1, 2 bar. It is within the scope of the invention that the inventive method is carried out at substantially atmospheric pressure. H hereby a time-consuming transfer of the separation surface is avoided in the vacuum, whereby the duration of the purification of the chlorosilane mixture is significantly reduced.

Since the deposition of polycrystalline silicon takes place only at temperatures above 600 ° C, the separation surface in step (a) in a further advantageous embodiment of the inventive method to a temperature of 600 ° C to 1000 ° C, preferably at 700 ° C. to 900 ° C, more preferably heated to 750 ° C to 850 ° C. Thus, the heating of the separation surface to a certain temperature allows the deposition rate of polycrystalline silicon on the Abscheidefläche and thus to selectively adjust a separation of impurities. In a further advantageous embodiment of the method according to the invention, the etching gas is hydrogen chloride. By bringing the separation surface into contact with hydrogen chloride, the polycrystalline silicon deposits formed thereon are converted into the gas phase to form an etching gas mixture.

A further aspect of the present invention is a device for removing impurities from chlorosilanes, in particular for carrying out a method according to one of claims 1 to 8, comprising:

A deposition chamber, which deposition chamber has at least one separation surface for depositing polycrystalline silicon, at least one gas inlet and at least one gas outlet, at least one fluid supply line, preferably gas supply line, which fluid supply line is connected to the gas inlet of the separation chamber and at least one fluid discharge line, preferably gas discharge line Fluid discharge line is connected to the gas outlet of the deposition chamber.

In a first advantageous embodiment of the invention, the deposition chamber has a heating device which serves for heating the separation surface and / or the fluid supply line and / or the fluid discharge line. This heating device may be formed, for example, as electrically operated coils which at least partially enclose the separation chamber and / or the fluid supply line and / or the fluid discharge line. However, the invention is not limited thereto.

For deposition of polycrystalline silicon on the separation surface, the heater serves in a second advantageous embodiment of the device to the Abscheidefläche to 600 ° C to 1000 ° C, preferably at 700 ° C to 900 ° C, more preferably 750 ° C to To heat 850 ° C.

It is within the scope of the invention that several heating zones can be formed by this heating device in order to optimize the formation of polycrystalline deposits. Advantageously, this is achieved in that only a small proportion of the chlorosilane is deposited as polycrystalline silicon on the deposition surface, so that the main part of the chlorosilane in the purified, gaseous chlorosilane mixture can be removed. At the same time, however, much of the contaminants can be concentrated in the small amount of polycrystalline silicon deposited. This advantageously results in a purification of the gaseous chlorosilane mixture with simultaneously low consumption of the silicon precursor compound. For example, a first heating zone may be formed in the region of the gas supply lines and / or the gas inlets in order to heat the gaseous chlorosilane mixture before it is brought into contact with the separation surface. Furthermore, the formation of several heating zones has a positive effect on the flow behavior of the gaseous chlorosilane mixture and / or the process gas in the separation chamber.

In a second advantageous embodiment of the device according to the invention, the separation chamber is designed as a hollow body with outer wall, which outer wall encloses an inner region of the deposition chamber, in which inner region at least one partition wall is arranged for guiding a gas flow.

In a further advantageous embodiment of the device according to the invention, the separation surface is at least partially disposed on the inner region of the outer wall of the deposition chamber facing the inner region and / or at least partially on the partition wall. Therefore, the partition wall serves not only to guide the gas flow but also to increase the separation area by allowing polycrystalline silicon to be formed not only on the inner wall side of the outer wall but also on the surface of the partition wall. Thus, the amount of deposited polycrystalline silicon on the deposition surface is increased.

In order to further increase the amount of polycrystalline silicon deposits and to extend the travel distance which the glass flux travels through the deposition chamber, the inner area of the deposition chamber has, in a further advantageous embodiment of the device according to the invention, a number of partitions which dividing walls Divide the Innenbereich such that a gas introduced into the deposition chamber meandering is guided through the deposition chamber, wherein preferably the partitions are arranged substantially perpendicular to the longitudinal axis of the deposition chamber. In a further preferred embodiment of the device according to the invention, the gas inlet and the gas outlet are arranged on two substantially opposite sides of the outer wall of the deposition chamber. Hereby it is achieved that the gas flow covers the maximum possible distance through the deposition chamber, whereby the amount of polycrystalline silicon deposits is further increased.

In order to further increase the separation area and thus to increase the intake quantity of the impurity, in particular of the dopant, the separation area is at least partially structured in a further advantageous embodiment of the device according to the invention.

In a further preferred embodiment of the device according to the invention, the separation surface has fins and / or channels in order to enlarge the surface.

The separation surface is formed in a further advantageous embodiment of the device according to the invention of graphite or silicon carbide.

Further advantageous features of the invention will become apparent from the following description of exemplary embodiments with reference to the drawing. Showing:

Figure 1 is a schematic representation of a first embodiment of a device according to the invention for the removal of impurities from chlorosilanes and

Figure 2 is a schematic representation of a second embodiment of a device according to the invention for the removal of impurities from chlorosilanes.

FIG. 1 shows a first exemplary embodiment of a device 1 according to the invention for removing impurities from chlorosilanes. This device Device 1 has a deposition chamber 2 and a separation surface 3. In the present exemplary embodiment, the separation surface 2 is formed from graphite. The deposition chamber 2 is designed as a hollow body with outer wall 4, which outer wall 4 encloses an inner region 5 of the deposition chamber 2. Furthermore, the separation chamber 2 has three gas inlets 6, 7, 8, which are connected to gas supply lines 9, 1 0, 1 1. About the gas inlets 6, 7, 8, a gaseous chlorosilane mixture, a process gas and an etching gas are temporally and / or spatially separated from each introduced into the deposition chamber 2. In the present exemplary embodiment, the deposition chamber 2 and the separation surface 3 have a temperature of 700 ° C. If the chlorosilane mixture is present as a liquid at room temperature, an optional evaporator (not shown) can be arranged on the gas supply line 9.

Furthermore, six partition walls 121, 122, 123, 124, 125, 126 for guiding a gas flow are arranged in the inner region 5 of the deposition chamber 2. These partitions 121, 122, 123, 124, 125, 126 subdivide the inner region 5 of the separation chamber 2 in such a way that a gas introduced into the deposition chamber 2 is guided meandering through the separation chamber 2. As is apparent from Figure 1, the partitions 121, 122, 123, 124, 125, 126 are arranged in the present embodiment perpendicular to the longitudinal axis of the deposition chamber 2. However, the invention is not limited to such an arrangement of the partitions 121, 122, 123, 124, 125, 126.

For discharging the purified, gaseous chlorosilane mixture and the gaseous etching gas mixture two gas outlets 1 3, 14 are arranged on the outer wall 4 of the deposition chamber 2, which gas outlets 1 3, 14 are each connected to a Gasausfuhrleitung 1 5, 1 6. The gas outlets 1 3, 14 are arranged on the separation chamber 2 in such a way that they face the three gas inlets 6, 7, 8. In this way, it is achieved that the gas flow through the deposition chamber covers a maximum possible distance, whereby the depletion of impurities and / or dopants is maximized. The sequence of an embodiment of the method according to the invention can be described as follows with reference to FIG. 1: In order to remove impurities and / or dopants from chlorosilanes, the separation surface 3 of the deposition chamber 2 in the present exemplary embodiment is heated to a temperature of 700 ° C. under atmospheric pressure. Depending on the composition of the gaseous chlorosilane mixture, however, the separation surface 3 can also be heated to a different temperature in the range from 600 ° C. to 1000 ° C. Subsequently, a gaseous chlorosilane mixture, which in the present embodiment contains a phosphorus-containing dopant and trichlorosilane, is introduced via the gas supply line 9 by means of the gas inlet 6 into the inner region 5 of the separation chamber 2. At the same time, a process gas is introduced into the separation chamber 2 via the gas inlet 8, which is connected to the gas supply line 11. However, it is also within the scope of the invention that the gaseous chlorosilane mixture and the process gas are introduced successively into the reaction chamber.

In the present exemplary embodiment, the chlorosilane mixture and the process gas of such type are introduced into the inner region 5 of the separation chamber 2 such that the chlorosilane mixture is present in a molar ratio of 3 mol% in the process gas. As a process gas of the separation chamber 2 high purity hydrogen is supplied.

Due to the temperature of 700 ° C it comes at the Abscheidefläche 3 of the deposition chamber 2 for the formation of polycrystalline silicon deposits, which polycrystalline silicon deposits are enriched with the phosphorus-containing dopant. Herein, the amount of spent chlorosilane is adjusted by the selected temperature and gas composition. The used here chlorosilane is no longer available as a productive gas. In which the dopant-containing chlorosilane mixture completely flows through the deposition chamber 2, it is almost completely freed from the dopant. The size of the active surface affects the cleaning efficiency of the device according to the invention. The purified, gaseous chlorosilane mixture is then by means of the gas outlet 1 3 via the Gasausfuhrleitung 1 5 from the separation chamber 2 discharged. In the present exemplary embodiment, the discharged, purified, gaseous chlorosilane mixture has a residual concentration of the dopant of 1 5 ppb. After the purified, gaseous chlorosilane mixture has been removed from the separation chamber 2, the deposition chamber is supplied with an etching gas via the gas inlet 7, which is connected to the gas supply line 10. In the present embodiment, hydrogen chloride is used as the etching gas. The hydrogen chloride fed to the deposition chamber 2 serves to return the polycrystalline silicon deposits and the dopant to the gas phase, whereby a gaseous etching gas mixture is formed. This gaseous etching gas mixture is discharged via the gas outlet 14, which is connected to the gas discharge line 1 6, from the deposition chamber 2. Thus, by means of the described method, a chlorosilane mixture contaminated with dopant can be alternately cleaned and the resulting polycrystalline silicon deposits removed from the deposition chamber 2.

As is further apparent from FIG. 1, the deposition chamber 2 has a heating device 17. This serves to heat the Abscheidefläche 3 to a temperature in the range of 600 ° C to 1000 ° C, whereby the deposition of polycrystalline silicon is made possible. This heater 1 7 is presently designed to be electrically operated coils. In the present exemplary embodiment, the deposition chamber 2 is surrounded almost completely by electrically operated coils (35 watt), which heats the separation surface 3 to 700.degree. However, the invention is not limited thereto. Other types of heaters may also be used.

FIG. 2 shows a second exemplary embodiment of a device 1 according to the invention for removing impurities from chlorosilanes. The device 1 has a structure largely identical to the embodiment described in FIG. 1, which is why it is not necessary to discuss further details at first. The deposition chamber 2 shown in Figure 2 has only one partition wall 121; however, it can be extended by further partitions, depending on requirements. As shown in Figure 2, the separation chamber 2 via the Gasausfuh rleitung 1 5 with a gas inlet 1 8 one of the deposition chamber 2 subsequent Device 1 9 are connected to chemical vapor epitaxy. Such a structure enables the gaseous chlorosilane mixture purified in the deposition chamber 2 to be fed to a subsequent chemical vapor phase epitaxy device 1 9 and used to form crystalline silicon layers. However, the invention is not limited to such an application.

Claims

claims

1 . Process for removing impurities, in particular dopants, from chlorosilanes, comprising the following steps:

(a) heating from a separation surface (3);

(b) contacting at least one gaseous chlorosilane mixture with the heated deposition surface (3), which gaseous chlorosilane mixture comprises at least one chlorosilane and at least one impurity, in particular at least one dopant;

(c) at least partially removing the impurity, in particular the dopant, by forming polycrystalline silicon deposits on the deposition surface (3), which polycrystalline silicon deposits are enriched with the impurity, in particular with the dopant;

(d) discharging the purified gaseous chlorosilane mixture;

(e) contacting an etching gas with the heated deposition surface (3) to return the polycrystalline silicon deposits and the contaminant, in particular the dopant, to the gas phase to form a gaseous etching gas mixture; and

(f) removing the gaseous etching gas mixture.

2. The method according to claim 1,

characterized,

in step (b) the contacting of the gaseous chlorosilane mixture and the separation surface (3) is effected in the presence of a process gas.

3. The method according to claim 1 or 2,

characterized,

that the process gas is hydrogen.

4. The method according to any one of claims 1 to 3,

characterized, in that the purified, gaseous chlorosilane mixture removed in step (d) has a residual concentration of the impurity, in particular of the dopant less than 1000 ppb, preferably less than 100 ppb, particularly preferably less than 1 ppb.

Method according to one of claims 1 to 4,

characterized,

that the chlorosilane is silicon tetrachloride and / or trichlorosilane and / or dichlorosilane.

Method according to one of claims 1 to 5,

characterized,

in that the formation of polycrystalline silicon deposits on the separation surface (3) takes place at a pressure of 0.8 to 1.2 bar, preferably at atmospheric pressure.

Method according to one of claims 1 to 6,

characterized,

the separation surface (3) is heated in step (a) to a temperature of 600 ° C to 1,000 ° C, preferably 700 ° C to 900 ° C, more preferably 750 ° C to 850 ° C.

Method according to one of claims 1 to 7,

characterized,

that the etching gas is hydrogen chloride.

Device (1) for removing impurities from chlorosilanes, in particular for carrying out a method according to one of claims 1 to 8, comprising:

- A deposition chamber (2), which deposition chamber (2) has at least one Abscheidefläche (3) for depositing polycrystalline silicon;

- At least one gas inlet (6, 7, 8) and at least one gas outlet (1 3, 14); - At least one fluid supply line (9, 10, 11), preferably gas supply line, which fluid supply line (9, 10, 11) with the gas inlet (6, 7, 8) of the deposition chamber (2) is connected; and

- At least one fluid discharge line (15, 16), preferably gas discharge line, which fluid discharge line (15, 16) is connected to the gas outlet (13, 14) of the deposition chamber.

10. Apparatus according to claim 9,

characterized,

in that the separation chamber (2) has a heating device (17), which heating device (17) serves for heating the separation surface (3) and / or the fluid supply line (9, 10, 11) and / or the fluid discharge line (15, 16).

11. The device according to claim 10,

characterized,

in that the heating device (17) is designed to heat the separation surface (3) to 600 ° C to 1000 ° C, preferably to 700 ° C to 900 ° C, particularly preferably to 750 ° C to 850 ° C.

12. Device according to one of claims 9 to 11,

characterized,

the separating chamber (2) is designed as a hollow body with outer wall (4), which outer wall (4) encloses an inner area (5) of the separating chamber (2), in which inner area (5) at least one dividing wall (121, 122, 123, 124 , 125, 126) for guiding a gas flow.

13. Device according to claim 12,

characterized,

that the separation surface (3) at least partially on the inner region

(6) facing side of the outer wall (4) of the deposition chamber (2) and / or at least partially on the partition wall (121, 122, 123, 124, 125, 126) is arranged.

14. Device according to claim 12 or 13,

characterized, in that the inner region (5) of the deposition chamber (2) has a plurality of partition walls (121, 122, 123, 124, 125, 126), which partition walls (121, 122, 123, 124, 125, 126) cover the inner region ( 5) in such a way that a gas introduced into the deposition chamber (2) is guided meandering through the separation chamber (2), wherein preferably the partitions (121, 122, 123, 124, 125, 126) are substantially perpendicular to the longitudinal axis of the separation chamber ( 2) are arranged. 5. Device according to one of claims 9 to 14,

characterized,

in that the gas inlet (6, 7, 8) and the gas outlet (13, 14) are arranged on two substantially opposite sides of the outer wall (4) of the separation chamber (2). 6. Device according to one of claims 9 to 1 5,

characterized,

that the separation surface (3) is at least partially structured. 7. Device according to one of claims 9 to 1 6,

characterized,

the separation surface (3) has lamellae and / or channels. 8. Device according to one of claims 9 to 1 7,

characterized,

the separation surface (3) is made of graphite or silicon carbide.